Preparation, Morphology And Properties Of All-organic Dielectric Materials Based On Poly(Vinylidene Fluoride)

Energy storage materials have attracted tremendous attention with improving living standards. High-k films are currently developed urgently as a new type of energy storage materials due to their excellent dielectric properties and large energy storage area. Because of the outstanding film-forming property and high energy storage capability of polymer, polymer-based dielectric materials have supplied a helpful approach to the development of energy storage films. In this paper, PVDF with high dielectric constant are used as matrix, and are blended with polar crystal PA to prepare all-polymer films with good dielectric performances through different processes and controlling methods of microstructure.The main research contents and results are listed as follows:1. PA/PVDF blends were prepared by melt blending three types of PA (PA6, PA66, PA11) and PVDF. FTIR, XRD, DSC and SEM results show that there is no chemical reaction between PA and PVDF and no obvious changes of crystal structure can be detected, but the crystal perfection is decreased.2. When PA 11 are chosen as main research system, the mechanical characterization results show that PA11/PVDF blends have excellent elongation and high tensile strength regardless of the blending ratio. The blends are uniaxially stretched, and when the alternate frequency ranges from 102 to 107, PA11/PVDF blends show perfect frequency and temperature stabilities. When the mass ratio of PA11 and PVDF is 20:80, the dielectric constant of PA11/PVDF blend is 25, which is 3 times of that of pure PVDF and 6 times of that of pure PA11. XRD analysis indicates that PVDF in uniaxially stretched PA11/PVDF blends induces large amount ofβcrystal.3. Strong polar small molecules DMSO are introduced into the PA 11/PVDF blends system and PA11/PVDF blends are prepared though solution blending. The strong polar effect of DMSO leads to the formation of moreβcrystal of PVDF in PA11/PVDF blends. When the ratio of DMSO-H2O is 5:95, the dielectric constant of PA11/PVDF blending film (PA11:PVDF=80:20) is as high as 188.1, but the dielectric loss is also as high as 1.37 at high alternate frequency due to the unstable chelating effect of DMSO to the blends system.4. PA11-g-GMA is obtained by small molecule grafting approach, and PA11-g-GMA/PVDF blend is then prepared through melt blending. The strong polar effect and the occurrence of grafting reaction makes the dielectric properties of blend materials improved greatly. Dielectric constant of 34 and dielectric loss less than 0.05, are obtained at the GMA content of 10%. The leakage current of the blend is lower than that of PA11/PVDF.5. Alternating copolymer of vinyl acetate and maleic anhydride (VA-MA) is prepared as macromolecule compatibilizer. VA-MA is reacted with PA11 to produce PA 11-g-VA-MA grafting copolymer which is then blended with PVDF, and the results show that PA11-g-VA-MA decreases the interfacial tension of the two phases and increases the compatibility of PVDF and PA11. However, the remarkable increase of compatibility does not improve the dielectric constant but decreases the dielectric loss of the blends system.6. Adding copolymer of styrene and maleic anhydride (SMA) to blend with PA11 and PVDF, when PA11/PVDF/SMA blends were uniaxially oriented by drawing can decreased the dielectric loss (tan8<0.07), increased dielectric constant(εbiend=59).The Voltage-Current test analysis found that the remnant current of PA11/PVDF blends is as low as10-7uA/cm2. The remnant current at 0 V of PA11/PVDF blend with SMA is an order of magnitude lower than that of PA 11/PVDF blend without SMA.The effect of macromolecular morphology alterations in responsive field on their electrical and charge storage properties can bring new possibilities into effect for functional composite materials.